Emissions of nitrous oxide (N₂O)—a greenhouse gas with a global warming potential approximately 300 times larger than carbon dioxide—continued unabated between 1980 and 2020, a year when more than 10-million metric tons were released into the atmosphere primarily through farming practices, according to a new report by the Global Carbon Project.

Global N₂O budget during 2010–2019. The colored arrows represent N₂O fluxes (in Tg N yr⁻¹ for 2010–2019) as follows: red – direct emissions from nitrogen additions in the agricultural sector (agriculture); orange – emissions from other direct anthropogenic sources; maroon – indirect emissions from anthropogenic nitrogen additions; brown – perturbed fluxes from changes in climate, CO₂, or land cover; and green – emissions from natural sources. The anthropogenic and natural N₂O sources are derived from BU estimates. The blue arrows represent the surface sink and the observed atmospheric chemical sink, about 1% of which occurs in the troposphere. The total budget (sources + sinks) does not exactly match the observed atmospheric accumulation, as each of the terms has been derived independently and we do not force TD agreement by rescaling the terms. This imbalance falls within the overall uncertainty in closing the N₂O budget, as reflected in each of the terms. The N₂O sources and sinks are given in teragrams of nitrogen per year (Tg N yr⁻¹). © The Global Carbon Project.

Agricultural production accounted for 74% of anthropogenic nitrous oxide emissions in the 2010s—attributed primarily to the use of commercial fertilizers and animal waste on croplands—according to the report “Global Nitrous Oxide Budget 2024”, led by researchers from Boston College and published in the journal Earth System Science Data.

In 2020 and 2021, nitrous oxide flowed into the atmosphere at a faster rate than at any other time in history. On Earth, excess nitrogen contributes to soil, water, and air pollution. In the atmosphere, it depletes the ozone layer, and exacerbates climate change.

Agricultural emissions reached 8 million metric tons in 2020, a 67% increase from the 4.8 million metric tons released in 1980, according to the study, the most comprehensive study of global nitrous oxide emissions and sinks produced by a team of 58 researchers from 55 organizations in 15 countries.

Nitrous oxide emissions from human activities must decline in order to limit global temperature rise to 2 °C as established by the Paris Agreement. Reducing nitrous oxide emissions is the only solution since at this point no technologies exist that can remove nitrous oxide from the atmosphere.

—lead author Hanqin Tian, the Schiller Institute Professor of Global Sustainability at Boston College

The concentration of atmospheric nitrous oxide reached 336 parts per billion in 2022, a 25% increase over pre-industrial levels that far outpaces predictions previously developed by the Intergovernmental Panel on Climate Change, said Tian.

The world’s farmers used 60 million metric tons of commercial nitrogen fertilizers in 1980. By 2020, the sector used 107 million metric tons. That same year, animal manure contributed 101 million metric tons for a combined 2020 usage of 208 million metric tons.

Drawing on millions of nitrous oxide measurements taken during the past four decades on land and in the atmosphere, freshwater systems, and the ocean, Tian said the researchers have generated the most comprehensive assessment of global nitrous oxide to date.

The researchers examined data collected around the world for all major economic activities that lead to nitrous oxide emissions and reported on 18 anthropogenic and natural sources and three absorbent sinks of global nitrous oxide. The top 10 nitrous oxide emission-producing countries are: China, India, the United States, Brazil, Russia, Pakistan, Australia, Indonesia, Turkey, and Canada, the researchers found.

Some countries have seen success implementing policies and practices to reduce nitrous oxide emissions, according to the report. Emissions in China have slowed since the mid 2010s; as have emissions in Europe during the past few decades. In the US, agricultural emissions continue to creep up while industrial emissions have declined slightly, leaving overall emissions rather flat.

Improved practices in agriculture around the use of nitrogen fertilizers and animal manure can help to address and reduce greenhouse gas emissions and water pollution.

While there have been some successful nitrogen reduction initiatives in different regions, we found an acceleration in the rate of nitrous oxide accumulation in the atmosphere in this decade. The growth rates of atmospheric nitrous oxide in 2020 and 2021 were higher than any previous observed year and more than 30% higher than the average rate of increase in the previous decade.

—Global Carbon Project Executive Director Josep Canadell, who is also a research scientist at CSIRO, Australia’s national science agency

Tian said there is a need for more frequent assessments so mitigation efforts can be targeted to high-emission regions and economic activities. An improved inventory of sources and sinks will be required if progress is going to be made toward the objectives of the Paris Agreement.

Resources

• Tian, H., Pan, N., Thompson, R. L., Canadell, J. G., Suntharalingam, P., Regnier, P., Davidson, E. A., Prather, M., Ciais, P., Muntean, M., Pan, S., Winiwarter, W., Zaehle, S., Zhou, F., Jackson, R. B., Bange, H. W., Berthet, S., Bian, Z., Bianchi, D., Bouwman, A. F., Buitenhuis, E. T., Dutton, G., Hu, M., Ito, A., Jain, A. K., Jeltsch-Thömmes, A., Joos, F., Kou-Giesbrecht, S., Krummel, P. B., Lan, X., Landolfi, A., Lauerwald, R., Li, Y., Lu, C., Maavara, T., Manizza, M., Millet, D. B., Mühle, J., Patra, P. K., Peters, G. P., Qin, X., Raymond, P., Resplandy, L., Rosentreter, J. A., Shi, H., Sun, Q., Tonina, D., Tubiello, F. N., van der Werf, G. R., Vuichard, N., Wang, J., Wells, K. C., Western, L. M., Wilson, C., Yang, J., Yao, Y., You, Y., and Zhu, Q.: Global nitrous oxide budget (1980–2020), Earth Syst. Sci. Data, 16, 2543–2604, doi: 10.5194/essd-16-2543-2024, 2024.